Have an idea of what to say if she's asking what you want, a basic idea of what a pose is. Don't engage conversation when you're drawing. Set a fixed time limit and tell her beforehand.
Take a break regularly, like every quarter or half-hour between series of short poses or longer ones. Have things to draw eat and drink ready, especially coffee, ask her if she wants some. Engage (purely formal) conversation during the breaks, what she does, etc... Tell her what you do as well, where you're trying to enter. Let her see the drawings if she wants to, don't be "oh I'm so ashamed I'm so bad XD", she's not here to comfort you.
I'm taking a course and the model usually gets dressed/undressed behind a folding screen, go straight to the "posing place", then go straight back behind it; they're not walking around naked. It depends on the person but have something like that ready, if just having an open room available nearby.
Have props ready, at least a chair. Of course block exterior view, but of course you need the daylight. Don't try to impose a very specific pose, only give directions if she asks some (or only very general ones, like "let's have seated poses for this series, here use this chair"). Don't be too picky or spend more than seconds on small details, like "move your right hand slightly to the left", etc. Even better, don't spend any at all.
Be careful about drafts, have a heat source ready if it might be a problem. Leave the money somewhere obvious, in an envelope or something, tell her where it is at the end and don't spend more time on that.
Basically make it easy for her. She should just come in, pose, and get out.
